Income from Investments - Net Impairment Losses Recognized in Earnings (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Net Investment Income [Line Items]
Total Other-than-temporary Impairment Losses	$ (1.1)	$ (25.8)	$ (11.0)
Available for sale, debt securities, other than temporary impairment loss	(2.0)	(23.8)	(6.6)
Fixed Maturities:
Net Investment Income [Line Items]
Total Other-than-temporary Impairment Losses	(0.1)	(25.8)	(6.4)
Equity Securities
Net Investment Income [Line Items]
Total Other-than-temporary Impairment Losses	(0.5)	0.0	(4.2)
Real Estate
Net Investment Income [Line Items]
Total Other-than-temporary Impairment Losses	0.0	0.0	(0.4)
Other Long-Term Investments
Net Investment Income [Line Items]
Total Other-than-temporary Impairment Losses	$ (0.5)	$ 0.0	$ 0.0